A field device of process automation is frequently serviced from a remote control room, i.e. parameters of the field device are set from a remote location. Such a situation arises e.g. when the field device has no on-site display unit, or because the user is not located on-site in the plant. German Patent DE 10 2010 029 655 describes the application of a web server in the field device.
The terminology “parameter” means, in such case, an actuating or influencing variable, which acts on the field device and, thus, changes the behavior of the field device or delivers information concerning the state of the field device. A nonexclusive list of parameters includes, in such case, measurement frequency, measurement time, measured value, calibration point in time, output signal, supplied energy, etc.
It can, however, be desired to service the field device on-site. For example, the changing of a parameter of the field device should be directly observed and performed by a user at the measuring point, for example, the field device is to be calibrated.
The adjusting of settings in the field device can, in such case, be effected, for example, by means of a mobile device. Such a mobile device includes a display unit, on which a service/display menu is presented. Via the service/display menu, settings can be effected in the field device or information can be downloaded from the field device. As a rule, service/display menus are hierarchically structured, in order to facilitate for the user the finding of the desired information.
Known from the state of the art are mobile devices, which can be connected to the field device directly by means of a cable or to a fieldbus, which, in turn, is connected with the field device. In the second case, the mobile device is connected indirectly with the field device. However, in process automation, field devices are frequently installed in difficultly reachable locations.
The state of the art also contains mobile devices with wireless connections for configuring field devices, for instance, the device “Field Xpert” of the group of firms, Endress+Hauser.
A problem, which arises especially in the case of bus-fed field devices, especially in the case of two conductor devices, is that the energy available in the field device limited. Since, most often, a high data transmission rate is accompanied by a high energy consumption, only a smaller data transmission rate can be implemented.
Even when enough energy is available for the field devices (for instance, through the application of four conductor devices or two conductor devices with external energy supply), a maximal data transmission rate is opposed by several factors, especially under process conditions, i.e. the specific conditions of process automation. Among these factors are distance from the hotspot (thus the source), number of clients (i.e. users of the wireless network), application of older standards, losses through disturbances, geometry of the antenna, unfavorable arrangement in a factory building, taking into consideration standards and guidelines (e.g. the ATEX guidelines), etc.
The FDT/DTM concept is frequently used in process automation. These acronyms stand for field device tool and device type manager. A DTM is, in principle, a driver. The DTM includes all functions, the structure, the parametering and the graphical user interface, including a help system for the field device or, possibly, the entire device family. In order that all DTMs of different manufacturers function correctly, the interfaces to the surrounding systems as well as to other DTMs must be clearly defined. An FDT is such an interface definition. An example of an FDT is the program “FieldCare” of the group of firms, Endress+Hauser. In order that a mobile device connected with a field device can correctly change parameters of the field device, it is necessary always to have the complete driver (DTM) including service/display menu on the mobile device. Since different field devices have different DTMs and different firmware versions of the field devices require possibly different DTMs, many different versions must be earlier stored in the mobile device. Also, frequently the particular firmware version of the field device is not known or is only known directly on-site. In the case of the DTM concept, one is limited to one platform (Windows, since version 2.0 via .net)
Also, an adjusting of the field device is possible via the Device Description Language (DDL). Via a corresponding Device Description (DD), some (standard) parameters of the field device can be changed. Also, a DD must be earlier installed. The DD must be interpreted by a suitable software tool, wherein different interpreters must be specifically programmed.